The present invention relates to photosensitive compositions which contain an additive component to influence one or more physical and/or chemical properties of the composition. Such properties can include, without limitation, storage stability, photospeed, ability to laminate and adhere to a substrate and ability to laminate over voids in a substrate. The additive can be added in a concentration to replace a portion or all of a component of the photosensitive composition, e.g., replacement of binder.
Photosensitive compositions particularly useful as photoresists are well known in the prior art. Conventionally these compositions are stored in roll form. The composition is adhered to a support film to form a two ply material such as disclosed in U.S. Pat. No. 4,293,635 or more conventionally in a three ply material such as U.S. Pat. No. 3,469,982 with the composition sandwiched between a support film and a cover sheet. The material is unwound from a roll and the cover sheet, if present, is removed from contact with the photosensitive composition prior to use in lamination to a substrate, e.g., in manufacture of printed circuit boards. In storage of the material a potential defect of cold flow exists. An excessive amount of cold flow results in the material becoming unacceptable, e.g., edge fusion occurs which prevents unwinding of a roll without damaging the continuity of the photopolymerizable composition.
Generally storability with minimization of cold flow is imparted by proper selection and formulation of the components of the photopolymerizable material. An exception to a need to formulate storage stability in a composition is disclosed in U.S. Pat. No. 3,867,153. This publication teaches hardening of the edges of the roll such as by exposure to actinic radiation which prevents cold flow with the photopolymerizable composition effectively sealed within the roll.
Use of an additive component to change physical properties in a composition is well known. One example is using beads as a filler in an organic polymer composition which may be optionally polymerizable as disclosed in U.S. Pat. No. 4,414,278. The polymeric beads are discrete, substantially nonswellable and crosslinked with an average diameter in the range of 0.7 to 20 .mu.m.
In contrast to the use of the highly crosslinked nonswellable beads in a composition are swellable microgels which are a separate and distinct component. Microgel is a term originated in the paint industry and it includes crosslinked spherical polymer molecules of high molecular weight such as of the order of 10.sup.9 to 10.sup.10 with a particle size of 0.05 to 1 micron in diameter prepared by emulsion polymerization. Crosslinking renders these microgels insoluble but capable of swelling in strong solvent without destroying the crosslinked structure. The preparation and use of such microgels is described, e.g., in British Pat. No. 967,051 and U.S. Pat. No. 3,895,082.
Use of a component described as a microgel in one type of photosensitive composition is disclosed in Japanese patent application No. 52,116301. The composition contains a major ingredient of a methacrylate ester and a microgel, a polymerizable monomer, a photoinitiator and a thermopolymerization inhibitor. The microgel is a rubber type substance obtained by a graft polymerization of a vinyl monomer with a so-called rubber type base material having particle diameter of 0.01 to 10 microns. This photosensitive composition is used for offset printing.
A delustering coating composition which contains fine particles is disclosed in U.S. Pat. No. 4,518,472. The composition is applied to a molded article to provide high abrasion resistance or scratch resistance. Such composition for coating is a liquid which differs from the solid films of the present invention.